Nontoxic combination therapy with amphotericin B (AmB) and 1,3-Bis(2-Chloroethyl)-1-nitrosourea (BCNU) cures a transplantable syngeneic leukemia in AKR mice. During 4 to 6 weeks after therapy, a quantitative cellular assay demonstrates an initial sharp decline in leukemic cells in the bone marrow, and then a stabilization of the number of leukemic cells. After 6 weeks, most of the animals are cured; some then develop meningeal leukemia. The cured animals are immune to further challenge. This system therefore provides: 1) a model to study the host-tumor relationship; 2) a model closely relevant to the development of central nervous system leukemia in human patients. The basis for AmB action in establishing these models, and also its potential usefulness in therapy, will be studied. The studies will center on the effects of AmB on single cells, and especially on cells of the immune system, in vitro and in vivo; and on effects of combinations of agents on the host-tumor balance.